Tap water contains a certain amount of solubilized ions which upon water evaporation eventually deposit as salts such as calcium carbonate on surfaces which are often in contact with said water, resulting in an anaesthetic aspect of said surfaces. This limescale formation and deposition phenomenon is even more acute in places where water is particularly hard.
It is well known in the art that limescale can be removed chemically with acidic solutions, and a great variety of acidic cleaning compositions have been described for this purpose.
However, in many instances acidic compositions may cause the problem that they present hazards to the surfaces treated therewith. Indeed the acids which are used in acidic compositions, such as phosphoric acid and the like can damage the surfaces being treated. In particular, some corrosion/staining may occur when metal surfaces such as aluminium, chromed steel or stainless steel are treated with such acids.
It is therefore an object of the present invention to obviate this issue in providing a cleaning composition possessing excellent limescale removing capacity while being safe to the surfaces treated therewith.
It is also desirable to formulate a composition particularly suitable to remove limescale in large appliances like automatic dish washers and washing machines. Indeed, limescale deposits in said appliances may build-up on the heater element making heat exchange more difficult. In other words, limescale deposits in said appliances are undesirable not only because they result in an anaesthetic aspect but also as said limescale deposits may result in higher consumption of energy, poorer machine performance and eventually malfunction.
It is thus a further object of the present invention to formulate a cleaning composition suitable to be used for removing limescale in large appliances, said composition possessing excellent limescale removing capacity while being safe to the surfaces treated therewith, especially metal surfaces like heating elements, walls, bottom and any inner part.
It has now been found that the above objects are met by formulating liquid compositions comprising an acid-stable thickener and a specific acidic system, i.e. maleic acid and a second acid which has a first pKa not exceeding 5, or mixtures thereof. Indeed it has been found that the compositions of the present invention comprising maleic acid, said second acid and said acid-stable thickener are significantly safer to the surfaces treated therewith, than the same compositions without said acid-stable thickener, while being also particularly effective in removing limescale. In other words, the use of acid-stable thickeners in an aqueous acidic liquid composition comprising maleic acid and said second acid improves surface safety of the surfaces treated with said composition. Furthermore, it has been found, in the broadest aspect of the present invention, that the use of an acid-stable thickener, in an aqueous acidic liquid composition comprising maleic acid improves limescale removing performance.
An advantage of the aqueous acidic liquid compositions of the present invention particularly suitable for removing limescale in large appliances such as automatic dish washers and/or washing machines is that said compositions provide excellent limescale removal on different types of limescale deposition present in said automatic dish washers and/or washing machines, e.g. on the severe limescale deposits which build up on the warm parts such as the heating element as well as on homogeneous lighter deposits which build up on the extended surfaces like the walls. The aqueous acidic liquid compositions according to the present invention allow to obtain better limescale removing performance at lower total acid level as compared to the powder/granular limescale removal compositions available on the market. Another advantage is that the aqueous acidic liquid compositions according to the present invention allow to prevent tough limescale encrustations build-up that provokes higher energy consumption, less washing effectiveness and possible damages to the machines.
A further advantage of this invention is that said compositions are safe to different hard-surfaces including metal surfaces such as aluminium, chromed steel or stainless steel as well as synthetic materials such as rubber hoses, plastic trays and polymeric connections that are for example found in large appliances.
EP-A-0 496 188 discloses a composition comprising nonionic surfactants together with maleic acid whereby good limescale removal is provided. Although EP-A-0 496 188 discloses thickeners in general as an optional ingredient, no levels are disclosed.
EP-A-601 990 discloses a self thickened acidic composition having a viscosity of 10 cps to 700 cps at 60 rpm shear rate at 20.degree. C. and comprising an organic acid or mixtures thereof, preferably maleic acid and a thickening system comprising from 0.5% to 15% by weight of the total composition of a mixture of a nonionic surfactant and a cationic surfactant. More particularly, EP-A-601 990 discloses compositions which are thickened without the use of a thickener compound.
U.S. Pat. No. 5,232,632 discloses foam liquid hard surface detergent compositions, suitable to be packed in a non-aerosol spray delivery package, comprising a mixture of zwitterionic and nonionic surfactants, a hydrophobic solvent, a polycarboxylate detergent builder and a polymeric shear thinning thickener such as xanthum gum. Preferred compositions have a pH of from 1 to 5.5, however no maleic acid is disclosed.
U.S. Pat. No. 4,891,150 discloses thickened acidic cleansing and descaling compositions. Thickening Is obtained by adding different surfactants or mixtures thereof. Pure thickeners such as xanthum gum are mentioned as not being suitable to be used in the acidic compositions disclosed in U.S. Pat. No. 4,891,150. No maleic acid is disclosed.
GB-A-2 106 927 discloses toilet bowl cleaners which have a pH between 2.2 and 3.5 and comprise a non-volatile water soluble organic acid such as dicarboxylic acids having from 2 to 3 carbon atoms, a detergent and a cellulose ether thickener, preferably methyl hydroxypropyl cellulose at levels of from 0.5% to 1.2% by weight of the total composition. GB 2 106 927 teaches away from the use of maleic acid. Indeed it is mentioned in it that maleic acid was not screened for its solubility because of its inherent toxicity.
WO 95/07957 discloses acidic cleansing compositions for cleaning hard surfaces, said compositions being particularly suitable to be applied thereto by means of spray-type dispensers. Said compositions comprise a strong acid alone or in combination with a weak acid, a surfactant and a thickening amount of an organic polymer thickener such as xanthum gum. Maleic acid and sulphamic acid are mentioned amongst the weak acids and sulphuric acid is mentioned amongst the strong acids. However no levels for the weak organic acids are disclosed in the description and no example discloses maleic acid.
EP-A-411 708 discloses an acidic aqueous liquid composition comprising a detergent, an organic acid having 2 to 10 carbon atoms, an aminoalkylenephosphonic and phosphoric acid. Indeed the addition of an aminoalkylenephosphonic and phosphoric acid on top of mixtures of acids likes succinic, glutaric and adinic acid, improves the safety of the acidic compositions for use on enamel surfaces. The compositions therein are microemulsions which may be thickened by the addition of a thickener such as alkyl cellulose. However the acidic system of the present invention comprising maleic acid at a given level and a second acid which has a first pKa not exceeding 5 is nowhere disclosed in EP-A-411 708.
None of the above mentioned prior art documents discloses the compositions of the present invention whereby improved limescale removal performance and improved safety to the surfaces treated therewith is achieved. Also none of the above mentioned prior art documents discloses the use of a thickened aqueous acidic liquid composition comprising maleic acid and a second acid which has a first pKa not exceeding 5, or mixtures thereof, for removing limescale in large appliances like automatic dish-washers and/or washing machines.